Age Determination of Female Redhead Ducks

Abstract

Eighty-seven fall-collected wings from female redhead ducks (Aythya americana) were assigned to the adult or juvenile group based on and tertial shape and wear. To obtain spring age-related characters from these fall-collected groupings, we considered parameters of flight feathers retained until after the first breeding season. Parameters measured included: markings on and width of greater secondary coverts, and length, weight, and diameter of primary feathers. The best age categorization was obtained with discriminant analysis based on a combination of the most accurately measured parameters. This analysis, applied to 81 wings with complete measurements, resulted in only 1 being incorrectly aged and 3 placed in a questionable category. Discriminant functions used with covert markings and the three 5th primary parameters were applied to 30 known-age juvenile, handreared redhead females; 28 were correctly aged, none was incorrectly aged, and only 2 were placed in the questionable category. J. WILDL. MANAGE. 39(2):256-263 To estimate the production of a given waterfowl breeding population, information is needed on the expected productivity of various age cohorts. Of particular importance is the productivity of yearling birds compared with that of older females. Most of the techniques used to distinguish firstyear birds from adults are not valid for most ducks in the spring, because adult growth and sexual development have been attained and identifying feathers have been replaced. Even with those external characters of waterfowl that are age-related in in the spring (e.g., eye color [Trauger 1974] and bill spots [Kuroda 1937, Dane 1968]), the overlap between adult and first-year birds diminishes the usefulness of these